Objective: Loneliness can have detrimental consequences for adolescent mental health and wellbeing. Previous, international, investigations of attachment to companion animals have reported positive effects of such bonds on adolescent loneliness. The current study aimed to determine the relationship between companion animal attachment and loneliness among Australian adolescents. Method: A geographically diverse sample of Australian adolescents (n = 283) was gathered via an online survey. Participants responded to demographic and animal ownership variables as well as measures of companion animal attachment, social support and loneliness. Results: A small, negative but nonsignificant relationship between companion animal attachment and loneliness was found suggesting that, as adolescents' attachment scores rose, loneliness scores tended to decrease. Further analyses revealed an unexpected moderating effect of ownership level on the relationship between companion animal attachment and loneliness. While a significant negative relationship between companion animal attachment and loneliness was observed for adolescents with a family pet, a subset of primary owners with extreme levels of attachment, heightened loneliness and lower social support scores was noted. Conclusion: For many adolescents having a family or shared pet may provide a positive influence on loneliness levels. However, parallels with literature presenting adverse effects of extreme attachment to companion animals within older populations suggest that for some adolescents the relationship is more complex.